Gate valves are positioned in pipe line systems to control the flow of liquids and slurdes. The diameter of the pipeline, and hence the gate valve, will depend on the consistency and volume of the fluid controlled. Higher volume fluid flows will require larger gate valves. One well known type of gate valve employs two generally cylindrical molded rubber valve liners which are coaxially aligned to define a flow passage for the controlled liquid. The valve liners typically have flanges which retain the liners within metal housings. A metal plate is cycled between the two liners to close off fluid flow. In passing between the liners the rubber is deformed to tightly engage against the gate and maintain the required seal. Such a seal has been effectively employed in a number of gate valve models. However, as the diameter of the valve passage is increased, the forces on the rubber and the degree of compression required to maintain a suitable seal increases. A greater compression of the rubber may cause accelerated wear on the liners. Use of thicker rubber liners is more costly and also presents additional problems of controlling and retaining the desired liner shape.
Gum rubber based elastomers can be compounded to have good resilient properties for conventional gate valve designs. Gum rubber valve liners are acceptable for use with fluids at ambient temperatures which contain only mild corrosives and no oil. However, at high temperatures or in highly corrosive environments, non-rubber elastomers are required which have less than satisfactory resilient properties.
Rigid metal rings having a right-angle cross section have been molded within the valve liners or connected to the interior face of the liner to restrict deformation or shield the rubber from contact with the moving gate respectively
Gate valve assemblies having liners which employ a downwardly extending tab which form a split seat to retain the gate in the closed position have been effectively used to prevent fluid release in the course of valve cycling.
What is needed is a gate valve assembly which may be manufactured economically in many sizes, which is durable and performs predictably and may be fabricated to sustain high temperature and corrosive environments.